1. Field of the Invention
The present invention relates to bituminous compositions. The present invention particularly relates to bituminous compositions including an elastomer component.
2. Background of the Art
A major proportion of the roofing felts applied nowadays are made of modified bituminous compositions, e.g., bituminous compositions comprising a bitumen component and an elastomer component, typically a styrenic block copolymer such as SBS (polystyrene-polybutadiene-polystyrene) SEBS (polystyrene-poly[ethylene-butylene]-polystyrene); SIS (polystyrene-polyisoprene-polystyrene) and SEPS (polystyrene-poly[ethylene-propylene]-polystyrene) and the like. Advantages of modified bituminous compositions over traditional systems (blown bitumen) include: improved fatigue resistance (the accommodation of repeated thermal movements of the roof); improved flexibility (especially at low temperature, enabling contractors to lay felt under colder weather conditions than with conventional bitumen); improved strength (to allow a reduction in the number of plies of felt by replacing in whole or part the traditional blown bitumen coated system); improved resistance to (permanent) deformation at short and longer loading times (so-called ‘walk-on-ability’); and improved elasticity, resulting in a greater capacity to bridge movement of crack and joints.
Although modified bituminous compositions satisfy all of the above requirements in as much as these materials having excellent high and low temperature properties (i.e. cold bending resistance at −30 to −25° C. and flow resistance at 80 to 100° C.), improvement is still desired.
A property of particular importance in roofing applications is the walk-on-ability mentioned before. In case of inadequate walk-on-ability, torching, which is one of the most widely used application methods for bituminous roofing felts, could lead to undesired surface effects and/or damage due to insufficient resistance to deformation. An assessment of the resistance of a composition to withstand such working traffic is currently ranked by the penetration value (ASTM D5-94) at 50° C. A reduction in PEN value, i.e. improving the resistance to deformation, whilst maintaining the performance properties and especially the low temperature properties would be highly desirous.
It has now been found that walk-on-ability of modified bituminous compositions may be improved without (significant) effect on the other performance properties of the compositions. As a result, modified bituminous compositions with an improved balance of properties are now available. Alternatively, modified bituminous compositions may now be made of relatively soft bitumen, that would otherwise have insufficient walk-on-ability (too high PEN value).